UICollectionView: performBatchUpdates example

ViewController.swift

//
//  ViewController.swift
//  collView2
//
//  Created by Gavin Koehler on 11/11/15.
//  Copyright © 2015 From Now On, LLC. All rights reserved.
//

import UIKit

extension CollectionType where Generator.Element: Hashable {
    // Returns the index paths of the elements which still exist after the subtraction
    func differenceWith(collectionToSubtract:[Self.Generator.Element]) -> [NSIndexPath] {
        return Set(self).subtract(Set(collectionToSubtract))
            .flatMap { self.indexOf($0) as? Int }
            .map { NSIndexPath(forItem: $0, inSection: 0) }
    }
}

class ViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView!
    
    var cellData = [String]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        for i in 0...10 {
            cellData.append("Cell #\(i)")
        }
        
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func addOnePressed(sender: AnyObject) {
//        cellData.insert("New Object", atIndex: 0)
//        collectionView.reloadData()
        
//        self.cellData.insert("New Object", atIndex: 0)
//        self.collectionView.insertItemsAtIndexPaths([NSIndexPath(forItem: 0, inSection: 0)])
        
        self.cellData.insert("New Object", atIndex: 0)
        collectionView.performBatchUpdates({ () -> Void in
            self.collectionView.insertItemsAtIndexPaths([NSIndexPath(forItem: 0, inSection: 0)])
        }, completion:nil)
    }

    @IBAction func addMultiple(sender: AnyObject) {
//        self.cellData.insertContentsOf(["New Object 0", "New Object 1", "New Object 2"], at: 0)
//        
//        self.collectionView.insertItemsAtIndexPaths([
//            NSIndexPath(forItem: 0, inSection: 0),
//            NSIndexPath(forItem: 1, inSection: 0),
//            NSIndexPath(forItem: 2, inSection: 0),
//            ])
        
        collectionView.performBatchUpdates({ () -> Void in
            self.cellData.insertContentsOf(["New Object 0", "New Object 1", "New Object 2"], at: 0)
            
            self.collectionView.insertItemsAtIndexPaths([
                NSIndexPath(forItem: 0, inSection: 0),
                NSIndexPath(forItem: 1, inSection: 0),
                NSIndexPath(forItem: 2, inSection: 0),
                ])
            
        }, completion: nil)

    }
    
    
    
    @IBAction func addSubtractMultiple(sender: AnyObject) {
        
        // 1. generate new data
        // 2. get index paths of new data vs. old data
        // 3. assign new data
        // 4. perform batch updates
        
        var newData = [String]()
        
        for i in 1...12 {
            newData.append("Cell #\(i)")
        }
        
        let subtracted = Set(cellData).subtract(Set(newData))
        let added = Set(newData).subtract(Set(cellData))
        
        print("Subtracted: \(subtracted)")
        print("Added: \(added)")
        
        let subtractedIndexPaths = cellData.differenceWith(newData)
        let addedIndexPaths = newData.differenceWith(cellData)
        
        print("subtractedIndexPaths: \(subtractedIndexPaths)")
        print("addedIndexPaths: \(addedIndexPaths)")
        
        cellData = newData
        
        collectionView.performBatchUpdates({ () -> Void in
            self.collectionView.deleteItemsAtIndexPaths(subtractedIndexPaths)
            self.collectionView.insertItemsAtIndexPaths(addedIndexPaths)
        }, completion: nil)
        
    }
    
    @IBAction func resetPressed(sender: AnyObject) {
        let newData = ["Item 1", "item 2"]
        
        let subtractedIndexPaths = cellData.differenceWith(newData)
        let addedIndexPaths = newData.differenceWith(cellData)
        
        cellData = newData
        
        collectionView.performBatchUpdates({ () -> Void in
            self.collectionView.deleteItemsAtIndexPaths(subtractedIndexPaths)
            self.collectionView.insertItemsAtIndexPaths(addedIndexPaths)
        }, completion: nil)
        
    }
}

extension ViewController : UICollectionViewDataSource {
    
    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return cellData.count
    }
    
    // The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! LabelCellCollectionViewCell
        cell.label.text = cellData[indexPath.item]
        return cell
    }
    
    
}

extension ViewController : UICollectionViewDelegate {
    
}